1,962 research outputs found
Warm thick target solar gamma-ray source revisited
The 1.63 MeV gamma-ray line of Ne-20 is sensitive to protons of lower energies than most other nuclear de-excitation lines. Its unexpected strength has been taken as evidence for a solar flare fast ion distribution that remains steep at low energies, and thus has a large total energy content. It has also been suggested that its strength might instead reflect the enhancement of ion lifetimes that occurs when ambient temperatures exceed 10(7) K. Here we revisit this idea ( a) recognising that ions may be effectively trapped in high temperature regions and (b) taking account of the contribution to the line of all ions above threshold. The strength of the 1.63 MeV line relative to other de-excitation lines has been used to estimate the steepness (e.g. energy power-law index) of the ion distribution. We show that these estimates must be significantly revised if primary ions are contained in a region with temperature in the few 10(7) K range, lower than found elsewhere. Such a region would almost certainly be coronal, so we also briefly review other arguments for and against coronal gamma-ray sources
Econometric modelling of competition between train ticket types
INTRODUCTION
The railways in Britain have a long history of using price discrimination backed up with product differentiation to significantly increase revenue over what might
be obtained in an undifferentiated market. Whilst not as sophisticated as the yield management systems widely used in the airline industry, rail ticketing strategies are continually evolving, with new products emerging, unsuccessful products discontinued and gradual refinement of others.
In recent years, there has been increased interest in modelling competition between different ticket types. The re-organisation of the railway industry in Great Britain has provided a greater commercial incentive to operators to price differentiate in order to maximise the revenue from their franchises. The policy of moderation of competition has allowed limited on-track competition, largely based around overlapping franchises but also with service extensions and new entrants, and this has stimulated product development and hence interest in
ticket choice. Partly in response to the greater commercialisation of the railway industry, particularly where here is a degree of market power, the regulatory
bodies have taken a greater interest in the range of tickets offered and their associated prices, travel restrictions and availability (SRA, 2003).
This paper reports on research which was conducted as part of an update to the Passenger Demand Forecasting Handbook (PDFH), which contains a forecasting framework and recommended demand parameters that are widely used in the railway industry in Great Britain (ATOC, 2002), and as part of a project to provide the Strategic Rail Authority with evidence on cross elasticities between ticket types for use in its review of how it regulates rail fares
Direct Demand Models of Air Travel: A Novel Approach to the Analysis of Stated Preference Data
This paper uses what has been termed the direct demand approach to obtain elasticity estimates from discrete choice Stated Preference data. The Stated Preference data relates to business travellers' choices between air and rail. The direct demand methodology is outlined and some potential advantages over the conventional disaggregate logit model are discussed. However, further research regarding the relative merits of the two approaches is recommended. The direct demand model is developed to explain variations in the demand for air travel as a function of variations in air headway and cost and in train journey time, frequency, interchange and cost. Relatively little has previously been published about the interaction between rail and air and the elasticities and variation in them which have been estimated are generally plausible. In particular, the results show that large improvements in rail journey times can have a very substantial impact on the demand for air travel and that the rail journey time cross-elasticity depends on satisfying a three hour journey time threshold
Dirty, Skewed, and Backwards: The Smectic - Phase Transition in Aerogel
We study the smectic AC transition in anisotropic and uniaxial disordered
environments, e.g., aerogel with an external field. We find very strange
behavior of translational correlations: the low-temperature, lower-symmetry
Smectic C phase is itless translationally ordered than the it high-temperature,
higher-symmetry Smectic A phase, with short-ranged and algebraic translational
correlations, respectively. Specifically, the A and C phase belong to the
quasi-long-ranged translationally ordered " XY Bragg glass '' and short-ranged
translationally ordered " m=1 Bragg glass '' phase, respectively. The AC phase
transition itself belongs to a new universality class, whose fixed points and
exponents we find in a d=5-epsilon expansion
Elasticity, fluctuations and vortex pinning in ferromagnetic superconductors: A "columnar elastic glass"
We study the elasticity, fluctuations and pinning of a putative spontaneous
vortex solid in ferromagnetic superconductors. Using a rigorous thermodynamic
argument, we show that in the idealized case of vanishing crystalline pinning
anisotropy the long-wavelength tilt modulus of such a vortex solid vanishes
identically, as guaranteed by the underlying rotational invariance. The
vanishing of the tilt modulus means that, to lowest order, the associated
tension elasticity is replaced by the softer, curvature elasticity. The effect
of this is to make the spontaneous vortex solid qualitatively more susceptible
to the disordering effects of thermal fluctuations and random pinning. We study
these effects, taking into account the nonlinear elasticity, that, in three
dimensions, is important at sufficiently long length scales, and showing that a
``columnar elastic glass'' phase of vortices results. This phase is controlled
by a previously unstudied zero-temperature fixed point and it is characterized
by elastic moduli that have universal strong wave-vector dependence out to
arbitrarily long length scales, leading to non-Hookean elasticity. We argue
that, although translationally disordered for weak disorder, the columnar
elastic glass is stable against the proliferation of dislocations and is
therefore a topologically ordered {\em elastic} glass. As a result, the
phenomenology of the spontaneous vortex state of isotropic magnetic
superconductors differs qualitatively from a conventional,
external-field-induced mixed state. For example, for weak external fields ,
the magnetic induction scales {\em universally} like , with .Comment: Minor editorial changes, version to be published in PRB, 39 pages, 7
figure
"Soft" Anharmonic Vortex Glass in Ferromagnetic Superconductors
Ferromagnetic order in superconductors can induce a {\em spontaneous} vortex
(SV) state. For external field , rotational symmetry guarantees a
vanishing tilt modulus of the SV solid, leading to drastically different
behavior than that of a conventional, external-field-induced vortex solid. We
show that quenched disorder and anharmonic effects lead to elastic moduli that
are wavevector-dependent out to arbitrarily long length scales, and non-Hookean
elasticity. The latter implies that for weak external fields , the magnetic
induction scales {\em universally} like , with
. For weak disorder, we predict the SV solid is a
topologically ordered vortex glass, in the ``columnar elastic glass''
universality class.Comment: minor corrections; version published in PR
A New Phase of Tethered Membranes: Tubules
We show that fluctuating tethered membranes with {\it any} intrinsic
anisotropy unavoidably exhibit a new phase between the previously predicted
``flat'' and ``crumpled'' phases, in high spatial dimensions where the
crumpled phase exists. In this new "tubule" phase, the membrane is crumpled in
one direction but extended nearly straight in the other. Its average thickness
is with the intrinsic size of the membrane. This phase
is more likely to persist down to than the crumpled phase. In Flory
theory, the universal exponent , which we conjecture is an exact
result. We study the elasticity and fluctuations of the tubule state, and the
transitions into it.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with
figures already inside text; unpacking instructions are at the top of file.
To appear in Phys. Rev. Lett. November (1995
Floating phase in a dissipative Josephson junction array
We consider dissipative quantum phase transitions in Josephson junction
arrays and show that the disordered phase in this extended system can be viewed
as an unusual floating phase in which the states of local -dimensional
elements (single Josephson junctions) can slide past each other despite
arbitrary range spatial couplings among them. The unusual character of the
metal-superconductor quantum critical point can be tested by measurements of
the current voltage characteristic. This may be the simplest and most natural
example of a floating phase.Comment: 4 pages, RevTex4. The revised version contains higher order
renormalization group equations and the corresponding phase diagra
Flocking Regimes in a Simple Lattice Model
We study a one-dimensional lattice flocking model incorporating all three of
the flocking criteria proposed by Reynolds [Computer Graphics vol.21 4 (1987)]:
alignment, centring and separation. The model generalises that introduced by O.
J. O' Loan and M. R. Evans [J. Phys. A. vol. 32 L99 (1999)]. We motivate the
dynamical rules by microscopic sampling considerations. The model exhibits
various flocking regimes: the alternating flock, the homogeneous flock and
dipole structures. We investigate these regimes numerically and within a
continuum mean-field theory.Comment: 24 pages 7 figure
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